UH/HH-1B,C,E,L,K,M (Bell 204/205) Huey/USMC “Slick” Helicopter

The Bell UH-1 Iroquois (nicknamed “Huey”) is a utility military helicopter powered by a single turboshaft engine, with two-blade main and tail rotors. The first member of the prolific Huey family, it was developed by Bell Helicopter to meet a United States Army’s 1952 requirement for a medical evacuation and utility helicopter, and first flew in 1956. The UH-1 was the first turbine-powered helicopter to enter production in 1960 for the United States military, and more than 16,000 have been built since.[1]
The Iroquois was originally designated HU-1, hence the Huey nickname, which has remained in common use, despite the official redesignation to UH-1 in 1962.[2] The UH-1 first saw service in combat operations during the Vietnam War, with around 7,000 helicopters deployed. The Bell 204 and 205 are Iroquois versions developed for the civil market.

In 1952, the U.S. Army identified a requirement for a new helicopter to serve as medical evacuation (MEDEVAC), instrument trainer, and general utility aircraft. The Army determined that current helicopters were too large, underpowered, or too complex to maintain easily. In November 1953, revised military requirements were submitted to the Department of the Army.[3] Twenty companies submitted designs in their bid for the contract, including Bell Helicopter with the Model 204 and Kaman Aircraft with a turbine-powered version of the H-43. On 23 February 1955, the Army announced its decision, selecting Bell to build three copies of the Model 204 for evaluation with the designation XH-40.[4]

Model 204[edit]
Main article: Bell 204/205
Powered by a prototype Lycoming YT53-L-1 (LTC1B-1) engine producing 700 shp (520 kW), the XH-40 first flew on 20 October 1956[5] at Fort Worth, Texas, with Bell’s chief test pilot, Floyd Carlson, at the controls. Two more prototypes were built in 1957, and the Army had previously ordered six YH-40 service test aircraft, even before the first prototype had flown.[3][6] In March 1960, the Army awarded Bell a production contract for 100 aircraft, which was designated as the HU-1A and officially named Iroquois after the Native American nations.[7]
The helicopter quickly developed a nickname derived from its designation of HU-1, which came to be pronounced as “Huey”. The reference became so popular that Bell began casting the name on the helicopter’s anti-torque pedals.[2] The official U.S. Army name was almost never used in practice.[8] After September 1962, the designation for all models was changed to UH-1 under a unified Department of Defense (DOD) designation system, but the nickname remained.
While glowing in praise for the helicopter’s advances over piston-engined helicopters, the Army reports from the service tests of the YH-40 found it to be underpowered with the production T53-L-1A powerplant producing a maximum continuous 770 shaft horsepower (570 kilowatts).[N 1] The Army indicated the need for improved follow-on models even as the first UH-1As were being delivered. In response, Bell proposed the UH-1B, equipped with the Lycoming T53-L-5 engine producing 960 shp (720 kW) and a longer cabin that could accommodate either seven passengers or four stretchers and a medical attendant. Army testing of the UH-1B started in November 1960, with the first production aircraft delivered in March 1961.[3]
Bell commenced development of the UH-1C in 1960 in order to correct aerodynamic deficiencies of the armed UH-1B. Bell fitted the UH-1C with a 1,100 shp (820 kW) T53-L-11 engine to provide the power needed to lift all weapons systems in use or under development. The Army would eventually refit all UH-1B aircraft with the same engine. A new rotor system was developed for the UH-1C to allow higher air speeds and reduce the incidence of retreating blade stall during diving engagements. The improved rotor resulted in better maneuverability and a slight speed increase.[6] The increased power and a larger diameter rotor required Bell’s engineers to design a new tail boom for the UH-1C. The longer tail boom incorporated a wider chord vertical fin on the tail rotor pylon and larger synchronized elevators.
Bell also introduced a dual hydraulic control system for redundancy as well as an improved inlet filter system for the dusty conditions found in southeast Asia. The UH-1C fuel capacity was increased to 242 US gallons (920 liters), and gross weight was raised to 9,500 lb (4,309 kg), giving a nominal useful load of 4,673 lb (2,120 kg). UH-1C production started in June 1966 with a total of 766 aircraft produced, including five for the Royal Australian Navy and five for Norway.
Model 205[edit]
Main article: Bell 204/205

Ventura County Sheriff’s Department Air Unit Fire Support Bell HH-1H
While earlier “short-body” Hueys were a success, the Army wanted a version that could carry more troops. Bell’s solution was to stretch the HU-1B fuselage by 41 in (104 cm) and use the extra space to fit four seats next to the transmission, facing out. Seating capacity increased to 15, including crew.[9] The enlarged cabin could also accommodate six stretchers and a medic, two more than the earlier models.[9] In place of the earlier model’s sliding side doors with a single window, larger doors were fitted which had two windows, plus a small hinged panel with an optional window, providing enhanced access to the cabin. The doors and hinged panels were quickly removable, allowing the Huey to be flown in a “doors off” configuration.
The Model 205 prototype flew on 16 August 1961.[10][11] Seven pre-production/prototype aircraft had been delivered for testing at Edwards AFB starting in March 1961. The 205 was initially equipped with a 44-foot (13.4 m) main rotor and a Lycoming T53-L-9 engine with 1,100 shp (820 kW). The rotor was lengthened to 48 feet (14.6 m) with a chord of 21 in (53 cm). The tailboom was also lengthened, in order to accommodate the longer rotor blades. Altogether, the modifications resulted in a gross weight capacity of 9,500 lb (4,309 kg). The Army ordered production of the 205 in 1963, produced with a T53-L-11 engine for its multi-fuel capability.[N 2][12] The prototypes were designated as YUH-1D and the production aircraft was designated as the UH-1D.
In 1966, Bell installed the 1,400 shp (1,000 kW) Lycoming T53-L-13 engine to provide more power for the aircraft. The pitot tube was relocated from the nose to the roof of the cockpit, to prevent damage during landing. Production models in this configuration were designated as the UH-1H.[8][13]
Marine Corps[edit]
In 1962, the United States Marine Corps held a competition to choose an assault support helicopter to replace the Cessna O-1 fixed-wing aircraft and the Kaman OH-43D helicopter. The winner was the UH-1B, which was already in service with the Army. The helicopter was designated the UH-1E and modified to meet Marine requirements. The major changes included the use of all-aluminum construction for corrosion resistance,[N 3] radios compatible with Marine Corps ground frequencies, a rotor brake for shipboard use to stop the rotor quickly on shutdown and a roof-mounted rescue hoist.
The UH-1E was first flown on 7 October 1963, and deliveries commenced 21 February 1964, with 192 aircraft completed. Due to production line realities at Bell, the UH-1E was produced in two different versions, both with the same UH-1E designation. The first 34 built were essentially UH-1B airframes with the Lycoming T53-L-11 engine producing 1,100 shp (820 kW). When Bell switched production to the UH-1C, the UH-1E production benefited from the same changes. The Marine Corps later upgraded UH-1E engines to the Lycoming T53-L-13, which produced 1,400 shp (1,000 kW), after the Army introduced the UH-1M and upgraded their UH-1C helicopters to the same engine.
Air Force[edit]
The United States Air Force’s (USAF) competition for a helicopter to be used for support on missile bases included a specific requirement to mandate the use of the General Electric T58 turboshaft as a powerplant. The Air Force had a large inventory of these engines on hand for its fleet of HH-3 Jolly Green Giant rescue helicopters and using the same engine for both helicopters would save costs. In response, Bell proposed an upgraded version of the 204B with the T58 engine. Because the T58 output shaft is at the rear, and was thus mounted in front of the transmission on the HH-3, it had to have a separate offset gearbox (SDG or speed decreaser gearbox) at the rear, and shafting to couple to the UH-1 transmission.
Twin–engine variants[edit]
The single–engine UH-1 variants were followed by the twin-engine UH-1N Twin Huey and years later the UH-1Y Venom. Bell began development of the UH-1N for Canada in 1968. It changed to the more powerful Pratt & Whitney Canada PT6T twin-engine set. The U.S. also ordered the helicopter with the U.S. Air Force receiving it in 1970. Canada’s military, the U.S. Marine Corps, and the U.S. Navy first received the model in 1971.[14]
In 1996, the USMC began the H-1 upgrade program by awarding a contract to Bell Helicopter for developing the improved UH-1Y and AH-1Zs variants.[15] The UH-1Y includes a lengthened cabin, four-blade rotor, and two more powerful GE T700 engines.[1] The UH-1Y entered service with the USMC in 2008.[16]
Design[edit]
The UH-1 has a metal fuselage of semi-monocoque construction with tubular landing skids and two rotor blades on the main rotor.[17] Early UH-1 models featured a single Lycoming T53 turboshaft engine in versions with power ratings from 700 shp (522 kW) to 1,400 shp (1,040 kW).[6] Later UH-1 and related models would feature twin engines and four-blade rotors.
All aircraft in the UH-1 family have similar construction. The UH-1H is the most-produced version, and is representative of all types. The main structure consists of two longitudinal main beams that run under the passenger cabin to the nose and back to the tail boom attachment point. The main beams are separated by transverse bulkheads and provide the supporting structure for the cabin, landing gear, under-floor fuel tanks, transmission, engine and tail boom. The main beams are joined at the lift beam, a short aluminum girder structure that is attached to the transmission via a lift link on the top and the cargo hook on the bottom and is located at the aircraft’s center of gravity. The lift beams were changed to steel later in the UH-1H’s life, due to cracking on high-time airframes. The semi-monocoque tail boom attaches to the fuselage with four bolts.[18]
The UH-1H’s dynamic components include the engine, transmission, rotor mast, main rotor blades, tail rotor driveshaft, and the 42-degree and 90-degree gearboxes. The transmission is of a planetary type and reduces the engine’s output to 324 rpm at the main rotor. The two-bladed, semi-rigid rotor design, with pre-coned and underslung blades, is a development of early Bell model designs, such as the Bell 47 with which it shares common design features, including a dampened stabilizer bar. The two-bladed system reduces storage space required for the aircraft, but at a cost of higher vibration levels. The two-bladed design is also responsible for the characteristic ‘Huey thump’ when the aircraft is in flight, which is particularly evident during descent and in turning flight. The tail rotor is driven from the main transmission, via the two directional gearboxes which provide a tail rotor speed approximately six times that of the main rotor to increase tail rotor effectiveness.[18]
The UH-1H also features a synchronized elevator on the tail boom, which is linked to the cyclic control and allows a wider center of gravity range. The standard fuel system consists of five interconnected fuel tanks, three of which are mounted behind the transmission and two of which are under the cabin floor. The landing gear consists of two arched cross tubes joining the skid tubes. The skids have replaceable sacrificial skid shoes to prevent wear of the skid tubes themselves. Skis and inflatable floats may be fitted.[18]

Typical armament for UH-1 gunship
Internal seating is made up of two pilot seats and additional seating for up to 13 passengers or crew in the cabin. The maximum seating arrangement consists of a four-man bench seat facing rearwards behind the pilot seats, facing a five-man bench seat in front of the transmission structure, with two, two-man bench seats facing outwards from the transmission structure on either side of the aircraft. All passenger seats are constructed of aluminum tube frames with canvas material seats, and are quickly removable and reconfigurable. The cabin may also be configured with up to six stretchers, an internal rescue hoist, auxiliary fuel tanks, spotlights, or many other mission kits. Access to the cabin is via two aft-sliding doors and two small, forward-hinged panels. The doors and hinged panels may be removed for flight or the doors may be pinned open. Pilot access is via individual hinged doors.[18]
While the five main fuel tanks are self-sealing, the UH-1H was not equipped with factory armor, although armored pilot seats were available.[18]
The UH-1H’s dual controls are conventional for a helicopter and consist of a single hydraulic system boosting the cyclic stick, collective lever and anti-torque pedals. The collective levers have integral throttles, although these are not used to control rotor rpm, which is automatically governed, but are used for starting and shutting down the engine. The cyclic and collective control the main rotor pitch through torque tube linkages to the swash plate, while the anti-torque pedals change the pitch of the tail rotor via a tensioned cable arrangement. Some UH-1Hs have been modified to replace the tail rotor control cables with torque tubes similar to the UH-1N Twin Huey.[18]

U.S. Navy[edit]
The US Navy began acquiring UH-1B helicopters from the Army and these aircraft were modified into gunships with special gun mounts and radar altimeters and were known as Seawolves in service with Navy Helicopter Attack (Light) (HA(L)-3). UH-1C helicopters were also acquired in the 1970s.[36][37] The Seawolves worked as a team with Navy river patrol operations.[38]
Four years after the disestablishment of HA(L)-3, the Navy determined that it still had a need for gunships, establishing two new Naval Reserve Helicopter Attack (Light) Squadrons as part of the newly formed Commander, Helicopter Wing Reserve (COMHELWINGRES) in 1976. Helicopter Attack Squadron (Light) Five (HA(L)-5), nicknamed the “Blue Hawks”, was established at Naval Air Station Point Mugu, California on the 11 June 1977 and its sister squadron, Helicopter Attack Squadron (Light) Four (HA(L)-4), known as the Red Wolves, was formed at Naval Air Station Norfolk, Virginia on 1 July 1976.[39]

Royal Thai Air Force special operation troops rappel from UH-1 during a demonstration on Children day 2013
XH-40: The initial Bell 204 prototype. Three prototypes were built, equipped with the Lycoming XT-53-L-1 engine of 700 shp (520 kW).[13]
YH-40: Six aircraft for evaluation, as XH-40 with 12-inch (300 mm) cabin stretch and other modifications.
Bell Model 533: One YH-40BF rebuilt as a flight test bed with turbojet engines and wings.
HU-1A: Initial Bell 204 production model, redesignated as the UH-1A in 1962.[13] 182 built.[65]
TH-1A: UH-1A with dual controls and blind-flying instruments, 14 conversions.[65]
XH-1A: A single UH-1A was redesignated for grenade launcher testing in 1960.[13]
HU-1B: Upgraded HU-1A, various external and rotor improvements. Redesignated UH-1B in 1962.[13] 1014 built plus four prototypes designated YUH-1B.[65]
NUH-1B: a single test aircraft, serial number 64-18261.[13]
UH-1C: The UH-1B gunship lacked the power necessary to carry weapons and ammunition and keep up with transport Hueys, and so Bell designed yet another Huey variant, the “UH-1C”, intended strictly for the gunship role. It is an UH-1B with improved engine, modified blades and rotor-head for better performance in the gunship role.[13] 767 built.[65]
YUH-1D: Seven pre-production prototypes of the UH-1D.
UH-1D: Initial Bell 205 production model (long fuselage version of the 204). Designed as a troop carrier to replace the CH-34 then in US Army service.[13] 2008 built many later converted to UH-1H standard.[65]
HH-1D: Army crash rescue variant of UH-1D.[13]
UH-1E: UH-1B/C for USMC with different avionics and equipment.[13] 192 built.[65]
NUH-1E: UH-1E configured for testing.
TH-1E: UH-1C configured for Marine Corps training. Twenty were built in 1965.[13]
UH-1F: UH-1B/C for USAF with General Electric T58-GE-3 engine of 1,325 shp (988 kW).[13] 120 built.[65]
TH-1F: Instrument and Rescue Trainer based on the UH-1F for the USAF.[13] 26 built.[65]

Base Rescue Moose Jaw CH-118 Iroquois helicopters at CFB Moose Jaw, 1982
UH-1H: Improved UH-1D with a Lycoming T53-L-13 engine of 1,400 shp (1,000 kW).[13] 5435 built.[65]
CUH-1H: Canadian Forces designation for the UH-1H utility transport helicopter. Redesignated CH-118.[13][66] A total of 10 built.[65]
EH-1H: Twenty-two aircraft converted by installation of AN/ARQ-33 radio intercept and jamming equipment for Project Quick Fix.
HH-1H: SAR variant for the USAF with rescue hoist.[13] A total of 30 built.[65]
JUH-1: Five UH-1Hs converted to SOTAS battlefield surveillance configuration with belly-mounted airborne radar.[13]
TH-1H: Recently modified UH-1Hs for use as basic helicopter flight trainers by the USAF.
HH-1K: Purpose built SAR variant of the Model 204 for the US Navy with USN avionics and equipment.[13] 27 built.[65]
TH-1L: Helicopter flight trainer based on the HH-1K for the USN. A total of 45 were built.[13]
UH-1L: Utility variant of the TH-1L. Eight were built.[13]
UH-1M: Gunship specific UH-1C upgrade with Lycoming T53-L-13 engine of 1,400 shp (1,000 kW).[13]
UH-1N: Initial Bell 212 production model, the Bell “Twin Pac” twin-engined Huey powered by Pratt & Whitney Canada T400-CP-400.[13]
UH-1P: UH-1F variant for USAF for special operations use and attack operations used solely by the USAF 20th Special Operations Squadron, “the Green Hornets”.[13]
EH-1U: No more than 2 UH-1H aircraft modified for Multiple Target Electronic Warfare System (MULTEWS).[67]
UH-1V: Aeromedical evacuation, rescue version for the US Army.[13]
EH-1X: Ten Electronic warfare UH-1Hs converted under “Quick Fix IIA”.[13]
UH-1Y: Upgraded variant developed from existing upgraded late model UH-1Ns, with additional emphasis on commonality with the AH-1Z.
Note: In U.S. service the G, J, Q, R, S, T, W and Z model designations are used by the AH-1. The UH-1 and AH-1 are considered members of the same H-1 series. The military does not use I (India) or O (Oscar) for aircraft designations to avoid confusion with “one” and “zero” respectively.